Escherichia coli is the most common cause of urinary tract infection. Its pathogenicity ranges from uncomplicated urethritis or cystitis to pyelonephritis with sepsis and endotoxemic shock. Capsular polysaccharides are believed to be important virulence determinants in a variety of microorganisms. In E. coli capsule has been attributed to play a role in the avoidance of killing by both complement and phagocytic cells. The majority of studies on capsular regulation, however, has been done on the group 1 capsule. Therefore we are undertaking studies in a pathogenic K54 isolate to gain insight on the regulation of group 2 capsule production. A more complete understanding of regulation of capsular synthesis may lead to improved or novel modalities for therapeutic intervention. Our approach in studying this question will be to use a combination of gene disruption and complementation experiments to evaluate the role, if any, of group 1 regulatory elements in the regulation of K54 (group 2) capsule synthesis. Once this is established we will be able to identify any novel regulatory proteins present in this pathogenic isolate.